the major head wake for anyone flying american airlines. 24 hours after they canceled more than 1,000 flights, abc's david kerley takes us inside the chaos. What caused the short circuit and what happened today. Reporter: This is what a computer crash looks like. Thousands of passengers in hours long lines. Planes grounded. 1,200 flights cancelled. Today, american airlines struggled to get back on schedule. Carlos maldano was trying, for a second day, to get home to new mexico. There was just one conflict after another, a lot of unhappy folks. Reporter: All the airline would say is that a software issue with its main and back up systems forced it to shut everything down. A stark reminder of how much our lives now need technology to work. We're so dependent on it now. So the convenience ends up backfiring sometimes. Reporter: It happened to united airlines last year as it was merging with continental and the two reservations systems. No shutdown, but severe delays. And guess what. American hopes to merge with u.S. Airways later this year. So after the computer glitch americans quickly took to youtube. We're very sorry for that. Reporter: Apologizing, but not promising that this will never happen again. David kerley, abc news, washington national airport.

This transcript has been automatically generated and may not be 100% accurate.